Pipette tips are elongate, typically conically tapering sleeves having a central through-opening extending along the longitudinal axis for the metering of small amounts of liquid. The pipette tips are slid at their wider end (coupling end) onto a suitable mount of a pipetting device and immersed with their pointed end, which axially opposes the wide end, into the medium to be pipetted. Typically, the pipette tips are intended for one-off use, i.e. they are discarded once they have been used.
Pipetting devices are used widely in all areas in which relatively small amounts of liquid (for example in the microliter range) have to be metered, for example in molecular biology. The pipetting device can be in the form of manual pipetting devices or pipetting machines or pipetting robots having an individual pipetting unit or a large number of individual pipetting units which are actuated at the same time or separately.
The basic mode of operation of a pipetting device is based on the fact that a defined volume of fluid is displaced, for example in a cylinder. The cylinder is in this case connected on the output side in an air-tight manner to the through-opening in the pipette tip, so that the displacement of the volume of fluid leads to a corresponding volume of the medium to be pipetted being drawn in at the pointed end of the pipette tip. In order to ensure precise metering, the pipette tip must be connected securely and tightly to the pipetting device. This is all the more necessary in the case of pipetting machines in which a secure fit and precise positioning of the individual pipette tips cannot be checked manually. In addition, it should be possible to manufacture pipetting devices in as low-maintenance and cost-effective a manner as possible.
A number of pipetting devices with holding devices for receiving pipette tips are known. Thus, for example, US 2002/094302, U.S. Pat. No. 4,679,446, DE 197 08 151 and U.S. Pat. No. 4,748,859 describe pipette tips having on the inner wall of their coupling end integrally formed peripheral sealing strips which seal the pipette tip radially against an outer circumferential surface of the mount. At the same time, lateral positional orientation of the pipette tip is intended to be attained in this way.
Complexly embodied radial seals are also described in US 2003/219359 and US 2004/011145. These seals consist of sealing lips which are formed integrally with the inner wall of the pipette tip and are intended to nestle against an outer circumferential surface of the mount. Nevertheless, the production costs for manufacturing the sealing lips are relatively high. In addition, the lateral fit of the pipette tip with sealing lips cannot be sufficiently ensured.
Axial orienting means can additionally be provided for orienting the pipette tips axially, i.e. in the z direction. These are described for example in U.S. Pat. No. 6,168,761, US 2003/082078, CA 2 122 244, U.S. Pat. No. 6,248,295, EP 148 333, U.S. Pat. Nos. 6,973,845 and 4,824,641.
All the aforementioned pipette tips are held by crimping the peripheral seal on the outer circumferential surface of the mount. U.S. Pat. No. 5,200,151, on the other hand, discloses fixing using separate locking ribs which are formed integrally with the inner wall of the through-opening in the pipette tip and engage after a locking mount encircling the outer circumferential surface of the mount.
A holding device with a rigid sealing collar is described in US 2003/0000319. This sealing collar interacts in the radial direction with a sealing surface of a pipette tip, the wall thickness of the pipette tip being sufficiently thin in the region of the sealing surfaces to ensure slight expansion during sliding onto the sealing collar.
EP 1 319 437 describes a holding device with an O-ring for radially sealing a pipette tip.
A radial seal between the pipette tip and holding device is described in EP 0 351 574 in which the holding device has a cylindrical sealing portion corresponding to a sealing portion of the pipette tip, the wall thickness in the region of the pipette tip-side sealing portion being thinner than adjacent regions, and thus flexible, in its configuration. This is achieved by a reduction in wall thickness on the inside and outside of the pipette wall. A pipette tip with a resilient cylindrical sealing portion is also described in WO 00/27530.
WO 00/62933 discloses a pipetting device having an annular crimp seal for radially sealing the pipette tip. For the purposes of sealing, a displaceable crimp sleeve is pressed onto the annular crimp seal, thus pressing said crimp seal radially outward into an annular groove formed on the inner wall of the through-opening in the pipette tip. A coupling sleeve, which has an annular stepped attachment and serves axially and radially to position the pipette tip, is arranged upstream of the crimp seal axially in the direction of the pipette tip. In the case of the pipetting device of WO 00/62933, the pipette tip is held and sealed by the crimp seal, although said crimp seal requires movable elements for actuation thereof. This leads to higher maintenance and appliance costs. Also, the crimp seal is subject to increased wear owing to the required flexing work.